1. Statement of the Technical Field
The present disclosure relates generally to respiratory interfaces, and more particularly to the field of respiratory medicine and to devices for use in delivering respiratory gases for therapeutic effect in high flow therapy.
2. Description of the Related Art
High flow therapy (HFT), also known as nasal insufflation, allows a large volume of respiratory gases to be administered for therapeutic use. The cannula for selected HFT devices is designed for high flow rates and to fit loosely in the nares of a patient so that the cannula does not form a seal. Since HFT is traditionally flow based (the flow rate is set), a seal could cause development of high and possibly dangerous pressures to form. Moreover, a seal may prevent proper exhalation.
Respiratory gas at these high flow rates is typically heated and humidified for patient comfort. The breathing gas may be room air or a mixture of air and oxygen.
Nasal cannulas are presently used for delivery of HFT, and it is reported that flow rates at these high levels generate pressures in the upper airway of a patient. The level of upper airway pressure generated during HFT using a standard nasal cannula is dependent on the size of the cannula and the open area around the cannula inside the nostril. For any size cannula, the level of upper airway pressure will vary according to the shape and size of the patient's nostrils. The flow rate of the gasses and the velocity of the flow also can affect airway pressures. A patient with large nares would have a wider orifice and thus a lower pressure would be created than a patient with the same cannula and smaller nares. The pressure created in the upper airway is reported to have a therapeutic effect for certain respiratory conditions and sleep disorders. Consequently, during HFT, it may be desirable to control and increase the pressure in upper airways of the patient.
The airway pressures of patients are rarely, measured or regulated during HFT due to the lack of a conveniently available device or system for clinicians to use. The usual practice is for clinicians to administer HFT with flow rates within the patient's comfort zone and then monitor vital signs, oxygen saturation, and other relevant parameters. There are, however, devices in development that can measure the airway pressures of a patient during HFT. These HFT devices point to the need for new types of patient interfaces e.g., nasal cannula that maximize control and safety in the development of airway pressures during HFT.
Moreover, some patients may be mouth breathers. With a patent nasal passage, a nasal cannula for HFT will create some upper airway pressure when a patient is breathing through the mouth; however, the created pressure will not be as high as the pressure of isolated nasal breathing. As such, mouth breathing is a further limitation to creating upper airway pressures which may be desirable for use in therapy. Nasal insufflation may have low efficacy in patients with nasal congestion or poorly defined nasal passages.